The present disclosure generally relates to emissive electrodes and methods of manufacture. In particular, the present disclosure generally relates to emissive electrodes comprising a barium neodymium oxide, lamps comprising same, and methods of manufacture.
There are a number of known methods and types of light sources or lamps. One type of fluorescent lamp is based on ionization of gaseous mercury held at low pressures, usually in the presence of a noble gas fill within an electrode discharge space, to generate UV and/or visible light. Traditionally, mercury-containing fluorescent lamps have been widely used because of their excellent efficiency and good color rendering. Recently, though there are attempts to replace mercury fluorescent lamps by new designs because of the perceived adverse environmental effect of mercury.
Newer methods have been proposed to either replace mercury with other environmental friendly chemicals or to decrease Hg concentration. One method of preparing an essentially mercury-free fluorescent lamp typically utilizes a mixture of gallium halides and/or gallium metal. Other metals and mixtures now employed comprise, e.g., zinc and/or indium, and their iodides and/or chlorides. It is believed that these metal halides offer advantages in that the reasonable vapor pressure of the metal halides can enhance the relatively low vapor pressure of metals in the temperature range of 20-200° C. In operation, these metal halides are excited and either emit UV/visible photons or chemically decompose upon the excitation energy. Furthermore, their products of decomposition emit their characteristic UV/visible spectra in the discharge. It is believed that, during lamp operation and between operation periods, there are metal halides, metal atoms, and halogen molecules/atoms in the gas phase of the lamp.
However, unfavorable interactions have been observed between the different lamp parts (e.g., glass envelope, lead wires, or emissive mixtures, etc.) and the ionized “halide plasma”, which contains many chemically strongly reactive species. Such unfavorable chemical interactions have resulted in the formation of colored precipitates on envelope walls, and evaporation of components of the emissive mixtures leads to reduced lamp lifetime. Colored deposits on envelope walls also can decrease light output by its own absorption and can chemically bind the dosed metal and/or halide. Furthermore, in discharge lamps, hot spot temperature can reach 1000-1200° C., and a tungsten wire filament itself can reach 600-700° C., both of which can result in a slow evaporation of components of the emissive mixture material. For instance, a key limiting fact in the use of known Ba/Ca/Sr triple oxides/carbonates emissive mixtures in such systems, is evaporation of Ba. In such mixtures, a relatively high Ba content is applied because of its work function-lowering effect; yet, Ba starts to evaporate at a lower temperature than the other components.
Therefore, despite the efforts described, there remains a need to develop improved emissive materials having lessened chemical interactions between the emissive mixture and the gaseous environments in lamps, and decreased evaporation of components of the emissive mixture.